1. Field of the Invention
The present invention is directed to a planar electrode having a plurality of sub-electrodes, of the type suitable for use as a neutral electrode for an HF surgery device, the sub-electrodes being disposed on one side of a flexible, common carrier.
2. Description of the Prior Art
Planar electrodes having a plurality of sub-electrodes of substantially the same size arranged on one side of a flexible-common carrier are described, for example, in European Application 0 308 690, German OS 36 23 293, and German OS 37 18 585. Monitoring circuits are standard in HF-surgery devices to avoid burning the patient upon the occurrence of an unintentional, partial removal (detachment) of the electrode from the body of the patient. If the electronic outlay for the monitoring circuit, which may for example measure sub-currents of each electrode, is to maintained low, one of the sub-electrodes of the multi-part electrode must be used as an auxiliary electrode for supplying an auxiliary current. Such measurements are based on the knowledge that sub-electrodes of identical size form sub-currents which are also of substantially the same size, given current flow with full-surface application of the electrodes on the skin of the patient. This is known as a symmetry measurement.
Experience has shown that an undesired detachment of the electrode from the body of the patient usually occurs along a release edge which proceeds on a straight line. On a case-by-case basis, such a release edge may intersect two of the sub-electrodes of the type known in the prior art and be oriented such that the remaining surfaces of both of the sub-electrodes which are still in contact with the patient's skin have equal areas. Since the currents from these partial areas will also be substantially the same size, a conventional symmetry measurement will not recognize that such a partial detachment has occurred.